The sarcophytol A was reported to exhibit anti-carcinogenic promotor activity [Cancer Surveys, 2, 540 (1983); Taisha, Vol. 25, Special Edition, Gan '88,3 (1988)] and anti-tumor activity [Japanese Patent Publication 20213/1988], whereby it has been regarded as a useful anti-tumor agent. As can be seen from the following structure, sarcophytol A is a cembrane type diterpene-alcohol containing one conjugated double bond and two other double bonds in the 14-membered ring. ##STR2##
The present inventors studied with the aim of developing a synthetic method of sarcophytol A and proposed a synthetic route shown by the following synthetic route 1 [JP Patent Appl. 181710/1989; filing date: Jul. 14, 1991]. ##STR3## wherein R.sup.7 is C.sub.1 -C.sub.4 lower alkyl group or phenyl group; X.sup.1 is a halogen atom or a leaving group such as OSO.sub.2 R.sup.9 and the like; R.sup.8 is a hydrogen atom, or trimethylsilyl group or 1-ethoxyethyl group; and R.sup.9 is lower alkyl group such as methyl group or ethyl group, substituted alkyl group such as trifluoromethyl group, phenyl group or substituted phenyl group such as toluyl group, mesityl group or the like.
Although the previously proposed method according to the above synthetic route 1 gives the objective sarcophytol A, it has some problems as follows:
1) it requires as the starting material a valuable compound (A), namely "E,E'-farnesol" of a structure essential for the production of sarcophytol A;
2) the oxidation of the terminal methyl group of compound (B) with selenium dioxide is poor in both the selectivity and yield.
3) the process to prepare the Compound (F) by reducing compound (D) to Compound (E), and oxidizing the latter is complicated and inefficient.
Thus, the process shown by the synthetic route 1, especially that concerned with the production of the intermediate (F) from the starting compound (A) is, not optimal for the industrial production of sarcophytol A, and a more efficient method for preparing the compound (F) has been demanded.
Under these circumstances, the present inventors have continuously investigated earnestly with the aim of developing a more efficient and simple method for producing the intermediate (F), thereby providing a process applicable to the industrial production of sarcophytol A, and have now found that certain novel substituted-acyclic terpene compounds are useful for the establishment of the purpose of the invention.